Effect of Niobium Microalloying on the Mechanical Properties in Grade R4 Mooring Chain Steel

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 55; no. 2; pp. 695 - 705
• Main Authors: Qiu, Liang, Li, Junru, Zhang, Pengfei, Wang, Leiying, Mei, Guojun
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.02.2024; Springer Nature B.V
• Subjects: Anisotropy; Characterization and Evaluation of Materials; Chemistry and Materials Science; Continuous casting; Dimpling; Docking and mooring gear; Impact strength; Low carbon steels; Low temperature; Materials Science; Mechanical properties; Metallic Materials; Microalloying; Nanotechnology; Niobium; Niobium carbide; Original Research Article; Precipitates; Structural Materials; Surfaces and Interfaces; Thin Films; Toughness
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-023-07278-4

The mooring chain is an important equipment to maintain the safety of marine facilities. In this study, the effect of niobium microalloying on the mechanical properties in R4 mooring chain steel 22MnCrNiMo is discussed. The effect of niobium microalloying on the anisotropy of mechanical properties of R4 mooring chain steel 22MnCrNiMo is thoroughly investigated. The anisotropy mechanism is analyzed. The results show that fine grain can be obtained by adding Nb. When Nb is increased from 0.038 to 0.23 pct, the grain cannot be made finer, and the mechanical properties of the test steel decrease slightly. A significant anisotropy in transverse and longitudinal mechanical properties of the experimental steel was observed because the impact toughness and tensile ductility were much lower in transverse specimens. Large-sized NbC precipitates degrade the mechanical properties of the experimental steel. Large-sized niobium carbide precipitates distributed along the transverse direction lead to the anisotropy of the experimental steel. The large-sized NbC precipitates are distributed in chains, which may be due to the segregation phenomenon caused by the enrichment of Nb and C during continuous casting. These chain-shaped precipitates make it easier for the microvoids in transverse specimens to interconnect with each other, resulting in the anisotropy of the experimental steel. The large-sized NbC precipitates promoted the transformation of microvoids to shallow chain-shaped dimples, which significantly reduced the low-temperature impact toughness and tensile plasticity in transverse specimens.